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Welding Aluminum vs. Welding Steel: Key Differences

Welding is a common technique for joining metal parts in various industries, such as construction, manufacturing, and automotive. However, not all metals are the same when it comes to welding. Aluminum and steel, for instance, have different properties and characteristics that affect the welding process and the quality of the welds. In this article, Megmeet Welding will explore some of the key differences between welding aluminum and welding steel, and how to overcome the challenges and achieve the best results.

I. Thermal Conductivity and Melting Point

One of the main differences between aluminum and steel is their thermal conductivity, which is the ability to conduct heat. Aluminum has a much higher thermal conductivity than steel, which means it transfers heat faster and more evenly. This can be an advantage for welding, as it reduces the risk of overheating and distortion of the metal. However, it also means that aluminum requires more heat input and a larger heat-affected zone to achieve a proper weld pool.

Another difference is the melting point of the metals. Aluminum has a lower melting point than steel, which is 1,221 degrees Fahrenheit compared to 2,500 degrees for steel. This means that aluminum can melt faster and easier than steel, but it also means that it can solidify faster and harder than steel. This can lead to cracking and porosity issues in the welds, especially if the welder does not control the cooling rate properly.

To deal with these differences, welders need to use the appropriate welding method, filler material, and shielding gas for the type of metal they are welding. For example, gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) are suitable methods for welding both aluminum and steel, but they require different filler materials and shielding gases.

  • For aluminum, welders should use a filler material that matches the base metal in terms of alloy and temper and a shielding gas that contains argon or a mixture of argon and helium.

  • For steel, welders should use a filler material that has a similar or slightly higher strength than the base metal, and a shielding gas that contains carbon dioxide or a mixture of carbon dioxide and argon.

II. Oxide Layer and Hydrogen Solubility

Another difference between aluminum and steel is the oxide layer that forms on the surface of the metal when it is exposed to air. Aluminum oxide is a hard and thin layer that protects the metal from corrosion and abrasion, but it also acts as an insulator that prevents the electric arc from penetrating the metal and creating a weld pool. Steel oxide, on the other hand, is a soft and thick layer that can be easily removed by the electric arc or by using a wire brush or a grinder.

  • To remove the oxide layer from aluminum, welders need to use a chemical or mechanical method before welding. A chemical method involves using a solvent or an acid to dissolve the oxide layer, while a mechanical method involves using a stainless steel brush or a scraper to scrape off the oxide layer. Welders should also use an alternating current (AC) when welding aluminum, as it helps to break up the oxide layer with its positive and negative cycles.

Another factor that affects the welding of aluminum is the hydrogen solubility in the metal. Hydrogen is very soluble in liquid aluminum, but not in solid aluminum. This means that when aluminum is melted during welding, it absorbs hydrogen from the atmosphere or from the filler material, and when it solidifies, it releases the hydrogen in the form of bubbles. These bubbles can cause porosity and weaken the welds.

  • To prevent hydrogen from entering the weld pool, welders need to use a clean and dry filler material and a shielding gas that does not contain any moisture or hydrocarbons. Welders should also avoid welding in humid or wet conditions, and store the filler material and the base metal in a dry and sealed place.

III. Conclusion

Welding aluminum and welding steel are different processes that require different skills and knowledge. Aluminum and steel have different properties and characteristics that affect the welding process and the quality of the welds. By understanding these differences and following the best practices for welding each metal, welders can achieve successful and durable welds.

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